Method of treating subsurface formations



murmbfi HZUU WE L'ITEQCI Fl aoii Jan, 20, 1959 A. s. MOKAY ET AL iETl-IOD FOR TREATING SUBSURFACE FORMATIONS Filed Sept. 14, 1954 wm w v. o +U P Q N v 0 A ma F United States Patent METHOD OF TREATING SUBSURFACE FORMATIONS Alexander S. McKay, Bellaire, Tex., and Edmond F.

Egan, New Orleans, La., assignors to The Texas Company, New York, N. Y., a corporation of Delaware Application September 14, 1954, Serial No. 456,002

9 Claims. (Cl. 1664) This invention relates to a method for treating a subsurface earth formation, formation section, or zone traversed by a well or bore hole and, more particularly, to a method of forcing or injecting a treating fluid into such a formation in such a manner that the injection of all of said fluid will be confined to the particular area desired. The principal object of the invention is the provision of a method of this type by means of which a fluid such, for example, as an acid can be forced into a desired formation such, for example, as an oil section of a permeable formation which formation also contains another fluid or fluids such as water or gas, while providing such accurate control of the fluid to be injected that all of it will pass into the oil section rather than into sections of the formation containing water or gas and without th necessity of using well packers.

Another object of the invention is the provision of a method for rendering substantially uniform the permeability of a subsurface formation or zone traversed by a bore hole in order to provide a good distribution pattern for water-flooding or secondary recovery operations.

This application is a continuation-in-part of our copending application Serial No. 349,924, filed April 20, 1953, now abandoned.

As one example of the application of the invention, it is known to be frequently desirable to force a material such as hydrochloric acid into the oil-containing portion of a formation where the formation consists mainly of a tight limestone. In many instances the oil-bearing section overlies a water-containing section of the formation, and frequently a gas-bearing section overlies the oil section. It is desirable, of course, that the acid be confined to the oil section so that the limestone will be dissolved or opened up to permit the oil to flow into the well. In the past, it has been necessary to provide rather complicated equipment, including flow tubing and packers set both above and below the oil section so that the acid flowing out of the tubing will enter the oil section without passing into the gas or Water section. This is obviously a time-consuming and expensive operation. Furthermore, the packers in the hole cannot control or direct the acid, once it leaves the hole, so as to confine it to the oil section.

As another example, the hydraulic rupturing or fracturing of oil formations has recently come into considerable use, and in this method a liquid under very high pressure is forced into a formation in such a manner that fractures or cracks are formed in the walls of the formation to increase the effective permeability and to permit oil or gas to flow more freely into the well. This operation has also required the use of carefully set packers.

The method to be described has proven to be capable of injecting fluids into formations with such accurate control that it now appears to be practicable for the first time to inject any given amount of fluid into any desired interval or area along the bore hole. This makes it possible to change the permeability or permeability profile of at Wed one which is more desirable. In the case of producing wells, one would presumably wish to increase the permeability opposite the oil-producing zones and to decrease the permeability opposite the water or gas-producing zones. In the case of water injection Wells in a water-flooding or secondary recovery operation, one would adjust the permeability profile so that the Water front would tend to move ahead uniformly at different depths in the oil-containing formation being flooded.

In accordance with the invention, the acid or other treating fluid to be injected into a predetermined formation or section is pumped downwardly in the bore hole through a pipe string to a depth substantially opposite the section into which the fluid is to be injected. Simultaneously therewith two other streams of fluid are pumped downwardly in the bore hole, one of these passing down through a string of tubing to a point below the formation section to be flooded while the other stream passes down through the annulus between the pipe string and the easing. The fluid to be injected into the desired formation or formation section has incorporated in it a substance which will render the fluid identifiable, and this spbgt apce may be a radioagtiy e traceiainthe form of ground carnotite,@ ac ti ggin e 9r t he like. With the three bodies of fluid in the hole, interfaces will exist between the traceable fluid and the fluid therebeneath and also between the traceable fluid and the upper fluid. Means are provided in the form of radiation detectors which can be passed through the bore hole, preferably through the tubing, for locating these interfaces in the bore hole. By adjusting or controlling the pumping rates of the three streams of fluid passing into the bore hole and by following the interfaces between the traceable fluid and the other fluid, the interfaces can be positioned and maintained at depths substantially opposite the upper and lower contacts or formation fluid interfaces in the formation containing the oil section. While the term fluid has been used, it is to be understood that the streams can be either of liquid or gas although liquid will generally be used.

When it is desired to increase the permeability of, say, a limestone formation, one usually injects acid into the formation as has been described. Since many formations have little vertical permeability it may be desirable to adjust the permeability of the formation over short steps of perhaps a few feet each. For example, one might wish to double the permeability of a three-foot interval. To do this the operator would place the two interfaces one at the top and the other at the bottom of this threefoot interval by adjusting the flow rates of the three streams. The acid would be introduced into the threefoot section between the two interfaces and the acid injection rate will be gradually increased in order to keep the two interfaces in their original position as the permeability of this section gradually increases. This process will be continued until the acid injection rate has increased to the amount that corresponds to the desired permeability of this three-foot section.

In the same manner described above in connection with the injection of acid, the permeability of any desired interval or section can be reduced by any desired amount when a suitable diluted plugging agent is used instead of the acid. Such a plugging agent may be a drilling mud, a mixture of bentonite and drilling mud or bentonite and drilling mud as a carrier for, say, ground limestone, cottonseed bulls and the like. The procedure is similar to that already described except that the injection rate of the plugging fluid will gradually be reduced in order to maintain the two interfaces in their original position and the plugging process will be stopped when the injection rate has fallen to the desired value.

In both the acidizing and the plugging processes it is necessary to spread the action over a reasonable amount of time while the positions of the interfaces are etermined by moving the radiation detectors every few minutes. If the permeability change brought about by the injection of acid or plugging material in the time interval that is required to locate the interfaces is too large, it may be necessary to inject the acid or the plugging material in slugs and to follow each slug by a comparatively large amount of other fluid. Each slug of plugging material will be small enough that it will accomplish only a small part of the desired permeability change but the process will be continued until the desired permeability has been attained.

In carrying out the invention in connection with a water-flooding or secondary recovery operation the steps set forth above can be repeated at different depths for injecting any desired fluid into the formation sections or zones; thus acid can be injected into one section to in crease its permeability, a plugging fluid into another section to decrease its permeability and so on, so that the ultimate result will be to render substantially uniform the permeability of the entire formation or zone to be used for water flooding.

Since with this method it is possible to place or spot almost any plugging agent in fluid form exactly where it is needed, the operation will be somewhat simpler when one desires to completely plug off a given section or interval. For example, fractured shale can be plugged with a mixture of drilling mud, ground limestone and cottonseed hulls, this material being injected into the section at gradually reduced rates until the two interfaces continue to spread apart at an extremely low rate of injection.

For a better understanding of the invention, reference may be had to the accompanying drawing in which Fig. 1 is a vertical sectional elevation of a well or bore hole traversing a permeable formation, while Fig. 2 is a diagrammatic vertical elevation showing a slightly modified form of the apparatus of Fig. 1.

Referring to the drawing, a bore hole is illustrated as passing through a formation 12 which may consist of a limestone and which may comprise water, oil and gasbearing sections. These sections are indicated respectively by the reference characters 14, 16, and 18. A formation fluid interface or contact will exist between the water and oil sections of the formation and another formation fluid interface 22 will exist between the oil and the gas-bearing section.

The upper portion of the well is provided with a conventional casing 24 closed at the top by means of a suitable casing head 26. Shown as passing down through the bore hole to a point approximately opposite the oil section 16 is a string of pipe 28 closed at its upper end as indicated at 30. Also extending down through the bore hole and preferably through the pipe 28 is a string of smaller tubing 32, this tubing extending to a point or depth preferably below the formation 12 or at least below the oil-bearing section 16. A pump 34 is connected to the pipe string 28 through a suitable meter 36 and serves to pump downwardly therethrough a treating fluid 38 such as hydrochloric acid to which a tracer such as a radioactive material has been previously added. A pump 40 is connected to the upper end of the tubing 32 through a meter 42 and serves to pump a non-radioactive liquid 44 downwardly into the bore hole through the tubing where it passes from the lower end at a point below the acid 38. An interface 46 will exist between the traceable fluid, i. e., the acid 38 and the liquid 44. The liquid 44 may be drilling mud and may have a higher density than the acid 38, although this is not always essential.

A third pump 46 is connected to the casing head 26 through the meter 48 and serves to pump another stream of non-radioactive liquid 50 downwardly through the annular space between the pipe string 28 and the casing 24 or the walls of the bore hole. The liquid 50 may be oil, having a density less than the acid 38. An interface 52 will likewise exist between the acid 38 and the upper liquid 50. By properly adjusting or controlling the pumping rates of the three liquid streams, the interfaces 46 and 52 can be moved up or down within the bore hole and either closer together or farther apart. By holding the interfaces 46 and 52 opposite the formation fluid interfaces 20 and 22 respectively, the acid 38 will be forced or squeezed into the oil section 16. The liquids 44 and 50 passing into the water and gas sections will confine the acid to the oil section.

Shown as suspended within the tubing 32 on a conductor cable 54 is a plurality, four in this instance, of gamma ray detectors indicated at 56, 58, 6t) and 62. These detectors are arranged in slightly separated pairs as is indicated in the drawing. The cable 54 passes upwardly over a suitable cable-measuring device 64 which will indicate or register continuously the depth of the radiation detectors in the bore hole. The cable then passes to an amplifying and recording device 66 which will record the outputs of the radiation detectors, preferably on am oving tape. If desired, separate recording devices may be used, one for each of the detectors 56, 58, 60 and 62.

As is shown in the drawing, the radiation detectors are connected to the conductor cable 54 in such a manner that the lower detectors 60 and 62 will be slightly sepaarted in a vertical direction and the upper pair of detectors 56 and 58 will be separated from the lower pair so that the mid-points between the two pairs of detectors will be spaced apart by the approximate thickness of the oil section 16.

In operation, the detectors may be run downwardly in the bore hole on the cable 54 to a depth such that the mid-points of the upper pair will be approximately opposite the oil-gas fluid interface or contact 22 and the mid-points of the lower pair of detectors will be approximately opposite the water-oil interface or contact 20. With the radiation detectors positioned in the hole as described, the pumps 34, 40 and 46 are adjusted to control the rates of pumping or injection of the three liquids 38, 44 and 50 so that the liquid interfaces 46 and 52 will be at the same depth or depths as the mid-points between the pairs of detectors 5658 and 69-62. In this position the detectors 56 and 62 will be opposite non-radioactive fluid while the other detectors 58 and 60 will be opposite the radioactive fluid 38, and the latter detectors will therefore have a considerably higher output than the detectors 56 and 62. This will be indicated in the record or records being made at 66. During this period, the radioactive fluid, i. e., the acid 38, will be forced into the oil section 16 while the nonradioactive fluids 44 and 50 will be forced into the water and gas sections 14 and 18 respectively. Since the three liquids are passing into the three sections at controlled rates, the acid 38 will be confined within the boundaries 20 and 22 of the oil section 16, and little, if any, of this acid will pass upwardly or downwardly into the gas or water sections 14 and 18. It is apparent that if packers were used above and below the body of acid 38, these packers would have no control over the flow of the acid after it leaves the bore hole, or, in other words, the acid could pass upwardly past the formation fluid interface 22 into the gas section and downwardly past the oil-water contact 20 into the water section.

Although the apparatus which has been described involves the use of two concentric strings of tubing 28 and 32, it is to be understood that this arrangement is not essential. Thus a somewhat simpler arrangement may be used such as is illustrated in Fig. 2. In this case the larger diameter pipe or tubing 28 is eliminated and the smaller tubing string 32a is shortened so that its lower end is opposite the formation or zone to be treated, for example, the oil section 16. A string of smaller diameter tubing or pipe 70, frequently referred to as a macaroni string, is attached to the outside of the tubing 32a in any suitable manner such as by clamping bands 72, and this string extends downwardly below the tubing 32a far enough so that its lower end will be below the contact plane 20.

If desired, the macaroni string 70 can be terminated opposite the zone 16 to be treated while the tubing 32a can extend down below the zone to be treated. In this case the radiation letectors can be kept at all times within the tubing 32a and will not be in direct contact with the acid.

The operation with the apparatus illustrated in Fig. 2 is substantially the same as that previously described with reference to the apparatus illustrated in Fig. l. The treating fluid is forced by means of pump 34a through the meter 36a and down the tubing string 32a so that it will pass out of the lower end thereof opposite the oil section 16. As is the case with the embodiment previously described, this treating fluid 38 may be made radioactive. At the same time a non-radioactive fluid 44 will be forced as by means of the pump 40a through the meter 42a and downwardly through the small string 70 from the lower end of which it will pass outwardly and into the water section 14, as indicated by the arrows. Simultaneously with the pumping of the fluids 38 and 44 the other non-radioactive fluid 50 will be forced by the pump 46a through the meter 48a and downwardly between the casing 24 and the exterior of the strings 32a and 70. The conductor cable 54 passes down through the tubing 32a and from this cable are suspended the radiation detectors 56, 58, 60 and 62 in the manner previously described. In this case the lower detectors 60 and 62 will hang down below the tubing string 32a but their function will be the same as that already set forth; that is, the detectors 6t) and 62 will, respectively, be above and below the interface 46 while the detectors 56 and 58 will, respectively, be above and below the interface 52 during the injection or treating operation, and as has been described, the operator in observing the responses of the detectors will adjust the pumping rates of the three fluid streams so as to maintain the upper interface 52 opposite the contact plane 22 and the lower interface 46 opposite the contact plane 20.

Although the lower liquid 44 has been described as having a density higher than the intermediate liquid 38 and the upper liquid 50 as having a density lower than the liquid 33, experience has shown that the desired interfaces can be maintained when the three liquids have the same density and even when the lower liquid is less dense than the one above it, providing that substantial flow rates are maintained. Thus, an acidizing operation can be conducted where water is used as the lower liquid 44 and also as the upper liquid 50.

While the invention has been described and illustrated as used in the acidization of an oil section lying between gas and water sections of the formation, it is to be understood that there are many instances where one of these fluids is not present. Thus, the formation may contain water and oil, oil and gas, or water and gas, and the method of the invention is equally applicable in situations of this kind. The principal purpose of the method is, as has been stated hereinbefore, to confine the injection of a particular fluid, such as an acid or a plugging fluid to a particular formation or formation section.

It is also to be understood that instead of utilizing four radiation detectors arranged in vertically separated pairs, as is shown in the drawing, the method can be carried out using a single detector by moving the detector up and down through the tubing 32 while observing the depth of the detector and by noting indications in the log or record that the detector is passing either the lower or the upper interface 46 or 52, respectively. Likewise, two detectors may be used and arranged on the cable 54 so that one detector will be substantially opposite the formation fluid interface 22 While the other will be opposite the interface 20.

Although the invention has been described generally with respect to the selective acidization of an oil formation or section, it is contemplated that the method can be used in many other ways. Recently considerable work has been done in formation fracturing and in such a method a liquid is forced under high pressure into a formation so as to rupture or provide cracks or fractures in the formation to increase its effective permeability and permit an easier flow of gas or oil into a well. The fracturing liquid usually contains sand which serves to fill and prop the fractures or crevices which are formed. It is contemplated in the present case that the treating liquid 38 may be a sand-containing oil or other liquid which it is desired to force into the section 18 to cause fracturing of the formation. The method of doing this would be substantially the same as has been described, or, in other words, the fracturing liquid 38 containing the propping material would be positioned between upper and lower liquids, all under high pressure, and the fracturing liquid containing the propping material would therefore be forced out into the resulting cracks or fractures in section 16. The fracturing liquid 38 could be made radioactive as described with reference to the acid, or, if desired, this liquid could be nonradioactive while both of the liquids 44 and 50 would be radioactive and the method for locating the interfaces 46 and 52 would be substantially that which has been described. Again, the fracturing liquid may be an acid.

While the intermediate liquid 38, i. e., the liquid to be injected into the desired formation or section, has been described as containing the radioactive tracer, it is to be understood that this is not essential and that the intermediate liquid 38 can be non-radioactive while the upper liquid 50 and the lower liquid 44 are made radioactive. It is merely necessary that the liquid at one side of each interface 46 or 52 be radioactive while the liquid of the other side is non-radioactive.

Again, although radioactive materials or tracers have been described as the means for identifying either the intermediate or the upper and the lower liquid streams, it is contemplated that either the intermediate liquid 38 or the upper and lower liquids 50 and 44 can contain a neutron reactive material such, for example, as a boron compound and that the interface between the boron-containing liquid and liquid which does not contain the boron can be located by incorporating Within a radiation detecting instrument housing a small source of neutrons. When neutrons from such a source pass outwardly into the surrounding liquid, gamma rays will be induced in the liquid and their intensity will depend upon whether the liquid contains the boron compound which, as is well known, will absorb a large number of the neutrons before they have a chance to induce gamma rays within the water. A method of this type for use in making an injectivity permeability profile log of a bore hole is disclosed in the copending application of E. F. Egan, Gerhard Herzog and A. S. McKay, Serial No. 463,998 filed October 22, 1954, as a continuation-in-part of Serial No. 349,817, filed April 20, 1953, now abandoned.

In addition to the method of uniformizing a formation or section one may wish to adjust the permeabilities of the various sections in such a way that they would be proportional to the porosities of the sections. This will apply either to permeability and/or porosity variations in a single formation or in different formations when the fluid is being simultaneously injected into more than one formation. This will tend to make the front of the water flood move along at the same rate in the different formations.

Obviously many other modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, but

7 only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. The method of rendering more uniform the permeability of the sections including too permeable sections and lesser permeable sections making up a predetermined formation traversed by an'uncased well bore hole, each of said sections having upper and lower boundaries, which comprises pumping a first stream oftreating fluid into said bore hole to a depth approximately opposite the section into which it is desired to inject said fluid, said fluid being selected from the. group consisting of acidizing fluids and plugging agent fluids having the property of changing the permeability of said section, simultaneously pumping second and third streams of fluid of a different character into said bore hole above and below the first-named fluid thereby producing interfaces between the body of the first-named fluid and the said second and third fluids respectively, locating 'saiclinterfaces and controlling the pumping rates of the three fluid streams so as to maintain said interfaces substantially opposite the upper and lower boundaries of said section, then changing the depth of the point of introduction of said treating fluid while simultaneously introducing said second and third fluids respectively above and below the treating fluid to establish interfaces at new locations to alter the permeability of another section and repeating said steps to thereby decrease the permeabilities of the too permeable sections While increaisng the permeabilities of the lesser permeable sections so that the perme abilities of the formation sections will be rendered more uniform.

2. The method of accurately injecting a given amount of treating fluid into a predetermined vertical interval of a permeable formation traversed by a well bore, which comprises pumping a metered stream of said treating fluid and introducing the same into said bore hole and into contact with the permeable formation at a depth approximately opposite said interval, simultaneously pumping a second stream of a non-treating, fluid and introducing the same into said bore hole and into contact with said permeable formation at a depth below that of said first named treating fluid introduction, simultaneously pumping a third stream of non-treating fluid and ,introducing the same into said bore hole and into contact with said permeable formation above said first named treating fluid, one of the group consisting of 1) said first named treating fluid and (2) said non-treating fluids containing a tracer material, positioning detecting means for said tracer material in said bore hole opposite the upper and lower extremities respectively of said predetermined vertical interval of the permeable formation, adjusting the pumping rates of said first and second streams to adjust and accurately locate the interface between said first named treating fluid and said non-treating fluid therebelow at said lower extremity, adjusting the pumping rate of said third stream relative to said first stream to adjust and accurately locate the interface between said first named treating fluid and said non-treating fluid thereabove at said upper extremity, and continuing the pumping of all three streams at rates to maintain said interfaces approximately at said upper and lower extremities respectively until the given amount of said first named treating fluid has been introduced into said predetermined vertical interval of the permeable formation.

3. The method as defined in claim 2, wherein said tracer material is a radioactive substance, and the positioning of said detecting means is accomplished by lowering into the bore hole to depth of said vertical interval two interconnected radiation detectors which are vertically spaced from each other a distance approximately equal to the length of said vertical interval.

4. The method as defined in claim 2, wherein said tracer material is a radioactive substance, and the positioning of said detecting means is accomplished by lowering into the bore hole to depth of said vertical interval four interconnected radiation detectors vertically arranged in two pairs, one pair being vertically separated from the otherpair by a distance approximately equal to the length of said vertical interval, and the detectors of each pair being vertically slightly separated from each other.

5. The method as defined in claim 2, wherein said first named treating fluid is an acid for increasing the permeability of said vertical interval of the formation, and wherein the acid injection rate is gradually increased relative to the pumping rates of said second and third streams as the permeability of said vertical interval of the formation increases.

6. The method asdefined in claim 2, wherein said first named treating fluid is a plugging material for decreasing the permeability of said vertical interval of the formation, and wherein the pumping rate of said plugging material stream is graduallyreduced relative to the pumping rates of said second and thirdstreams until finally the said two interfaces tend to spread apart at a low pumping rate of said plugging material stream.

7. The method as defined in claim 2, wherein said first named treating fluid is a liquid containing a propping agent which is thus spotted in the well bore at the desired location, and the resulting fluid column including the said spotted liquid containing the propping agent is then placed under sufiicient pressure to effect fracturing of the formation surrounding the well bore which is contacted by said fluid column, whereby the said liquid containing the propping agent penetrates any fractures formed along said predetermined interval and the propping agent will then maintain open any such fractures formed along the predetermined interval when said pressure is released.

8. The method in the fracturing of a formation traversed by a well bore which comprises spotting a treating fluid containinga propping material within a predetermined vertical extent of the well bore while confining thesaid treating fluid to within the upper and lower boundaries of said vertical extent by the injection of fluid essentially free of propping material into the well bore both above and below the said treating fluid to establish upper and lower interfaces between said treating fluid and said second mentioned fluid within said predetermined vertical extent, and applying sufficient pressure on the resulting fluid column in the well bore to result in fracture of the formation contacted by said fluid column, whereby any introduction of propping material into resulting cracks in the formation is essentially confined to that portion of the formation opposite the said predetermined vertical extent of the well bore.

9. The method in the fracturing of a formation traversed by a well bore which comprises injecting a treating fluid containing a propping material into a well bore intermediate upper and lower bodies of injected fluid essentially free from propping material to establish upper and lower interfaces between the said treating fluid and the said other fluid, locating the said interfaces and adjusting the positions of said interfaces to lie within upper and lower boundaries of a predetermined vertical extent of the well bore, and then applying sufficient pressure to the resulting fluid column in the well bore to result in fracture of any formation, whereby the introduction of propping material into the resulting cracks in the formation is essentially confined to that portion of the formation opposite the said predetermined extent of the well bore.

References Cited in the file of this patent UNITED STATES PATENTS 2,259,429 Simmons Oct. 14, 1941 2,450,265 Wolf Sept. 28, 1948 2,524,933 Silverman Oct. 10, 1950 2,596,843 Farris May 13, 1952 2,676,662 Ritzmann Apr. 27, 1954 2,700,734 Egan et al Jan. 25, 1955 

